Known from the state of the art as exemplified in Offenlegungsschrift (Laid-open application) WO 2011028220 A2 is a measuring apparatus for monitoring a protective tube. A measuring transducer applied directly on the protective tube is used for registering vibrations. This requires, however, a corresponding separate or additional measuring transducer, which is connected with the protective tube. This leads, thus, to extra costs and to a special construction of the measuring apparatus, especially an additional connection between protective tube and connection head, respectively transmitter electronics.
In general, there is in the case of an immersion body protruding into a flow the problem that vibrations caused by the flow in the worst case can lead to a tearing off of the immersion body. This is true not only for protective tubes for a thermometer but also for other apparatuses, for example, in the case of an immersion body, such as is used in the case of thermal flow measurement or for pH-value determination.
A tearing off of or a leak in the immersion body can lead to the failure of the measuring apparatus and even to shut down of the process running in a plant.